Emulsion explosive composition

ABSTRACT

An explosive emulsion composition which includes two oxygen supplying salts and urea as a discontinuous phase, and a continuous water-immiscible organic phase which consists predominantly of iso-paraffinic oils and one or more emulsifying agents.

FIELD OF THE INVENTION

[0001] The present invention relates to an explosive composition of the kind comprising a discontinuous oxidizer phase dispersed throughout a continuous fuel phase, which is substantially immiscible within the discontinuous phase. The explosive compositions of the present invention are especially suitable for use in the gold mining industry, among other mining and non-mining applications in which explosives are utilized.

BACKGROUND ART

[0002] Commercially available explosive emulsion compositions generally comprise an external or continuous organic fuel phase, in which discrete droplets of an aqueous solution of an oxidizer-supplying source are dispersed as an internal or discontinuous phase.

[0003] Explosive emulsion compositions may be manufactured with in-line motionless mixers or any type of mixer able to disperse the aqueous oxidizer phase into fine droplets with a typical size range of about 0.1 to 20 microns. In order to achieve such a fine droplet size distribution the inclusion of a suitable emulsifier in the mixture is deemed essential. The emulsifier is selected to promote subdivision of the droplets of the oxidizer phase and dispersion thereof in the continuous phase.

[0004] As background to this invention, reference is made to the following prior art: U.S. Pat. No. 4,338,146 (Granlund), EP 0460952 (Ireco Incorporated), GB 2298420 (Dyno Nobel Inc.), AU 566666 (Norsk Hydro A.S. ) and CA 2011491 (Pacific Patent Holdings Ltd).

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a graph depicting the effect on viscosity of iso-paraffinic oils v. n-paraffinic oils according to the present invention; and

[0006]FIG. 2 is a table comparing the stability of iso-paraffinic oils v. paraffinic oils according to the present invention.

SUMMARY OF THE INVENTION

[0007] It is an object of this invention to provide an explosive emulsion composition having a long shelf life, and which minimizes prior art problems of relatively poor performance in the areas of gassed emulsion blend lifetime, water resistance and viscosity increase upon pumping.

[0008] Surprisingly, it has been found that an explosive emulsion comprised of a disperse phase with two oxygen-releasing or -supplying salts and urea in an aqueous solution, and a continuous phase comprised of predominantly iso-paraffinic oils and a polymeric emulsifier, provides a substantial increase in performance in gassed blend lifetime and water resistance, and minimal viscosity increase upon a mixing test designed to replicate pumping. The term “iso-paraffinic oil” is defined herein as comprising hydrocarbons having a significant proportion of branched alkyl groups attached to the hydrocarbon backbone. This is in contrast to n-paraffinic oil, in which the hydrocarbon compounds are linear or straight-chain, and which are unbranched.

DETAILED DESCRIPTION OF THE INVENTION

[0009] According to one aspect of the present invention, there is provided an explosive emulsion composition comprising two oxygen-releasing salts plus a urea component as a discontinuous phase, while the fuel is comprised of predominantly iso-paraffinic lubricating oils and a polymeric emulsifier as a continuous phase. The composition may be made by emulsifying an aqueous solution or melt containing two oxygen-releasing salts and urea with a water immiscible fuel component comprising iso-paraffinic oils and a polymeric emulsifier to form an emulsion in which the oxidizing salts form part of the discontinuous phase, and the iso-paraffinic oils and the polymeric emulsifier form at least part of the continuous phase.

[0010] The oxidizer salts are preferably selected from the group consisting of ammonium, alkaline-earth nitrates and alkali metal nitrates. Preferably, the oxidizer salts are ammonium nitrate (AN) in combination with calcium nitrate (CN) or sodium nitrate (SN), together with urea, and mixtures thereof. The amount of oxidizer salt(s) employed is generally from about 50% to about 94%, by weight, and preferably from about 60% to about 85%, by weight, of the total composition. Accordingly, this invention relates to a water-in-oil emulsion composition comprising two salts plus urea in the discontinuous aqueous phase. It has been found that a composition of ammonium nitrate, sodium nitrate and urea provides a very stable emulsion.

[0011] More specifically, this invention relates to the use of iso-paraffinic oils in a continuous phase combined with the proper pH and a carefully selected catalyst in the discontinuous phase, to provide an emulsion having excellent stability with regard to shelf life, water resistance and stress resistance in both the neat emulsion and as a mixture with ammonium nitrate or an ammonium nitrate fuel oil mixture (ANFO) (the so-called “dry addition”).

[0012] As can be seen from Table 1, formulations MN001 and MN002 show enhanced stability. The stability of gassed blends in both cases were rated 6 after 35 days, which indicates a low level of crystallization and hence relatively high stability. Also, as the enclosed graph of FIG. 1 shows, there was a minimal viscosity increase after mixing of both emulsion matrices (MN001 and MN002). An increase of only a few thousand centipoises (cPs) was obtained after mixing for 3 minutes@1500 r.p.m. This test simulates the pumping of a product from a truck in the field. This is a very important measure or indicator of success from the standpoint of a field application, since an explosives delivery truck can handle emulsions much more easily and readily which do not exhibit a tendency to increased viscosity during pumping.

[0013] When the performances of MN001 and MN002 are compared with the remainder of the emulsions (MN003, MN004, MN005, MN006 and MN007) from Table 1, it is very clear that highly significant differences exist with regards to the stability of gassed blends and the tendency to increased viscosity after mixing.

[0014] It has been shown that the differences in the stability of gassed blends and the tendency to increases in viscosity after mixing is due to variation in the ratio between iso-paraffinic oils and paraffinic oils in the fuel phase. It has also been shown that the higher the percentage of iso-paraffinic oils in the fuel phase as compared to paraffinic oils, the better the stability of the gassed blends and the smaller the viscosity increase after the mixing test which simulates pumping.

[0015] The fuel phases employed were the same with the exception that the ratios between iso-paraffinic oil and paraffinic oil were varied to demonstrate the differences in performance achievable by the invention.

[0016] It is believed that the relatively small viscosity increase exhibited during the mixing test of emulsion matrices containing a high level of iso-paraffinic oils compared to n-paraffinics is a contributing factor in obtaining an exceptionally high water resistance. Without being limited by theory, it is speculated that the differences in chemical structure of iso-paraffinic oils compared to n-paraffinic oils is another contributing factor to the increased water resistance of such emulsions and emulsion blends.

[0017] The immiscible liquid organic fuel forming the continuous phase of the composition is present in an amount of from about 1% to about 10%, by weight, and, preferably, in an amount of from about 3% to about 8%, by weight, of the total composition. Suitable organic media that are capable of existing in the liquid state at convenient emulsion formulation temperatures include saturated or unsaturated aliphatic, alicyclic and/or aromatic hydrocarbons, and mixtures thereof. Preferred media include refined (white) mineral oil, diesel oil, petroleum distillates, benzene, toluene, styrene, xylenes, and mixtures thereof. The most preferred media are mineral oils which are comprised of hydrocarbons with a significant amount of alkyl chain branching. Such oils are commercially available from petroleum companies and include the Process Oils P830, P832, P833, P835, P836, P844, P857, P870, P873 and P874 available from The Shell Company of Australia Limited; HVI 500B, Motiva Star 3, Shellflex 2210, Shellflex 2310, Shellflex 2790, Shellflex 6131, and Shellflex 6212 available -from Shell Oil Products U.S.; and the Isopar Performance Fluids available from ExxonMobil, amongst others Urea comprises from about 1% to about 15%, by weight, and preferably from 3% to 9%, by weight, of the total composition.

[0018] This invention relates to the fuel phase comprising at least one emulsifier, and a mixture of hydrocarbons and lubricant oils. The emulsifier(s) are selected from the group of so-called PIBSA (poly (isobutylene) succinic anhydride) derivatives with organic amines or alkanolamines.

[0019] The hydrocarbon oil(s) in the continuous phase of the emulsion are predominantly of iso-paraffinic character, with some aromatic and naphthenic character. Specifically, in this invention, and as opposed to conventional wisdom, the use of iso-paraffinic oils (instead of n-paraffinic oils), when combined with two oxygen-releasing salts plus urea, dramatically increase the stability of the resulting emulsion, and hence improves its shelf life, water resistance and its resistance to a rise in its viscosity upon mixing.

[0020] The emulsifying agent(s) comprises from about 0.3% to about 3.5%, by weight, and preferably from about 0.5% to 1.5%, by weight, of the total composition. Water comprises from about 5% to about 25%, by weight, but preferably from 10% to 20%, by weight, of the total composition.

[0021] The present invention includes compositions formed by the method of “dry addition” to emulsions manufactured according to the method disclosed herein. A typical dry addition comprises ammonium nitrate or a blend of ammonium nitrate and diesel oil.

[0022] Preferably, the explosive emulsion composition according to the present invention includes a density reducing agent, selected from the group consisting of salts of alkali metal nitrites, which are employed in an amount sufficient to result in a composition having a density in the range of about 0.50 to about 1.39 g/cm³, but preferably between about 0.90 to about 1.39 g/cm³.

[0023] The invention also relates to a process for the preparation of emulsions comprising a discontinuous aqueous phase with two oxygen-releasing salts and urea, and a continuous water-immiscible fuel phase comprising a PIBSA derivative as an emulsifying agent and a majority of iso-paraffinic lubricating oils, the process comprising the steps of:

[0024] a) dissolving said oxygen-releasing salts plus urea in water at a temperature above the fudge point of the aqueous salt solution;

[0025] b) adjusting the pH of the oxygen-releasing salt mixture within the range of about 2.0 to about 7.0, preferably between about 3.5 and about 6.0, and most preferably between 5.0 and 5.5, and mixing with said organic fuel phase comprised of a derivative of a PIBSA emulsifier and iso-paraffinic oil(s) to form a uniform emulsion; and

[0026] c) adding a sufficient quantity of a density reducing agent to achieve the desired density.

[0027] In a preferred embodiment of the invention, the explosive emulsion composition further includes a gassing catalyst in the discontinuous phase, preferably selected from the group consisting of thiocyanates, preferably comprising from about 0.1% to about 1%, by weight, of the total composition.

[0028] In a further embodiment, the explosive composition is formed by dry addition, with the dry addition comprising between about 1% to about 95% by weight of the total composition. Preferably, the dry addition comprises ammonium nitrate prill, or a blend of ammonium nitrate prill and diesel oil (“ANFO”).

[0029] The explosive emulsion may also include a density reducing agent, for example selected from the group consisting of salts of alkali metal nitrites. Preferably, sufficient density reducing agent is used to yield a composition having a density in the range of about 0.50 to about 1.39 g/cm³.

BEST MODE OF CARRYING OUT THE INVENTION

[0030] The invention will now be described with reference to the following non-limiting examples, and with regard to the graph of FIG. 1 and Table 1, as set forth in FIG. 2.

[0031] In the preparation of the exemplified compositions of the present invention, the hydrocarbon oils were used in combination with lubricating oils. The lubricating oils contained a substantial amount of iso-paraffins. In certain cases a blend of straight n-paraffinic oils were used. (Refer to rating table for stability difference.)

[0032] The results obtained demonstrate that the greater the proportion of iso-paraffinic oils, the better the stability of the emulsion and the water resistance. The differences could be seen most clearly in respect of so-called gassed blends. Density reducing agents were employed to reach the desired density level. The explosive emulsion compositions are obtained as stable pumpable mixtures.

EXAMPLE

[0033] Oxidizer/Fuel Ratio: 94 6 COMPONENT LIQUOR PERCENTAGE MASS (g) Ammonium Nitrate 73.50 69.09 Sodium Nitrate 7.00 6.58 Urea 3.00 2.82 Catalyst for 0.30 0.28 chemical gassing (50% aqueous) H₂O 16.15 15.18 Citric Acid 0.05 0.05 (50% aqueous) TOTAL 100.00 94.00

[0034] The catalyst for chemical gassing is selected from the thiocyanate group of compounds.

Temp 78±2° C.

pH=5.25±0.25

[0035] Component Percentage Mass (g) Fuel COMPONENT FUEL PERCENTAGE MASS (g) PIBSA Emulsifier 10.00 0.60 Anfomul 2500 10.00 0.60 P874 50.00 3.00 P833 30.00 1.80 TOTAL 100.00 6.00 TOTAL 100.00

[0036] Anfomul 2500 is a PIBSA derivative reacted with an alkanolamine available from Croda Surfactants (U.K.). P833 is a mineral oil with a viscosity of 22.2 centistokes at 40° C. and P874 is a mineral oil with a viscosity of 4.1 mm²/s at 40° C. Both oils are available from The Shell Oil Company of Australia Limited.

TEMP 63±2° C.

cP of Oxidiser=57-59° C.

[0037] Although exemplary embodiments of the present invention have been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications or alterations to the invention described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications, and alterations should therefore be seen as being within the scope of the present invention.

[0038] It should be appreciated that the present invention provides a substantial advance in explosive emulsion compositions providing all of the herein-described advantages without incurring any relative disadvantages. 

What is claimed is:
 1. An explosive emulsion composition comprising an aqueous solution of two oxygen-releasing salts and urea in a discontinuous phase, and a continuous water-immiscible organic fuel phase comprising predominantly at least one iso-paraffinic oil and at least one emulsifying agent.
 2. The explosive emulsion composition according to claim 1, wherein said oxygen-releasing salts are selected from the group consisting of ammonium nitrate, sodium nitrate, calcium nitrate and urea, and mixtures thereof.
 3. The explosive emulsion composition according to claim 1, wherein the oxygen-releasing salt component comprises from about 50% to about 94%, by weight, of the total composition.
 4. The explosive emulsion composition according to claim 1, wherein urea comprises from about 1% to about 15%, by weight, of the total composition.
 5. The explosive emulsion composition according to claim 1, wherein said continuous water-immiscible organic phase comprises from about 1% to about 10%, by weight, of the total composition.
 6. The explosive emulsion composition according to claim 1, wherein said continuous water-immiscible organic phase comprises at least one derivative of poly(isobutylene) succinic anhydride and an amine or alkanolamine-emulsifier.
 7. The explosive emulsion composition according to claim 1, wherein said emulsifying agent comprises from about 0.3% to about 35%, by weight, of the total composition.
 8. The explosive composition according to claim 3, wherein the oxygen-releasing salt component comprises from about 60% to about 85%, by weight, of the total composition.
 9. The explosive composition according to claim 4, wherein urea comprises from about 3% to about 9%, by weight, of the total composition.
 10. The explosive emulsion composition according to claim 5, wherein said continuous water-immiscible organic phase comprises from about 3% to about 7%, by weight, of the composition.
 11. The explosive composition according to claim 7, wherein said emulsifying agent comprises from about 0.5% to about 1.5%, by weight, of the total composition.
 12. The explosive emulsion composition according to claim 1, wherein said water-immiscible organic phase comprises from about 1% to about 10%, by weight, of the total composition.
 13. The explosive emulsion composition according to claim 12, wherein said continuous water-immiscible organic phase comprises from about 3% to about 8%, by weight, of the total composition.
 14. A process for producing an explosive emulsion composition, which comprises: a) dissolving two oxygen-releasing salts and urea in water at a temperature above the fudge point of the aqueous solution; b) adjusting the pH of said oxygen-releasing salt and urea mixture between about 2 and 7; c) combining said oxygen-releasing salts and urea mixture and an organic fuel phase comprising a derivative of a polyisobutylene succinic anhydride emulsifier and iso-paraffinic oils; d) mixing until a uniform emulsion is formed; and e) adding a density reducing agent.
 15. A process for producing an explosive emulsion composition according to claim 1, which comprises: a) dissolving said oxygen-releasing salts and urea in water at a temperature above the fudge point of the aqueous solution; b) adjusting the pH of said oxygen-releasing salt mixture between about 2 and about 7; c) combining said oxygen-releasing salts and urea mixture and an organic fuel phase comprising a derivative of PIBSA emulsifier and iso-paraffinic oils; d) mixing until a uniform emulsion is formed; and e) adding a density reducing agent.
 16. The explosive emulsion composition according to claim 1, further including a gassing catalyst in the discontinuous phase.
 17. The explosive emulsion composition according to claim 16, wherein the gassing catalyst is selected from the group consisting of thiocyanates.
 18. The explosive emulsion composition according to claim 16, wherein the gassing catalyst comprises from about 0.1% to about 1%, by weight, of the total composition.
 19. The explosive emulsion composition according to claim 1, which is formed by dry addition, said dry addition comprising between about 1% to about 95%, by weight, of the total composition.
 20. The explosive emulsion composition according to claim 19, wherein the dry addition comprises ammonium nitrate prill, or a blend of ammonium nitrate prill and diesel oil (“ANFO”).
 21. The explosive emulsion composition according to claim 1, and including a density reducing agent.
 22. The explosive emulsion composition according to claim 21, wherein said density reducing agent is selected from the group consisting of salts of alkali metal nitrites.
 23. The explosive emulsion composition according to claim 21, wherein a sufficient quantity of a density reducing agent is used to yield a composition having a density in the range of about 0.50 to about 1.39 g/cm³.
 24. The process according to claim 14, wherein the pH is adjusted to between about 3.5 and about 6.0.
 25. The process according to claim 14, wherein the pH is adjusted to between 5.0 and 5.5. 